Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy.
In a typical canister purge operation, a canister purge valve coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
However, engine run time in PHEVs may be limited, and thus opportunities for purging fuel vapor from the canister may also be limited. It may be possible to force the engine on to allow for a purging operation, but this would decrease the overall fuel economy of the vehicle. Further, if the vehicle is parked during a portion of the diurnal cycle in which the ambient temperature is increasing, the fuel tank may undergo a pressure rise, forcing hydrocarbons out of the canister and into the atmosphere. This could potentially result in the vehicle failing emissions testing, and potentially losing classification as a practically zero emissions vehicle (PZEV).
The inventors herein have recognized the above limitations and have developed systems and methods to at least partially address these problems. In one example, a method for a plug-in hybrid electric vehicle, comprising: during a first condition, including an engine-off condition and the plug-in hybrid electric vehicle coupled to an external power source; heating a fuel vapor canister based on a fuel tank vacuum; and opening a fuel tank isolation valve to draw heated vapors into a fuel tank. In this way, a passive purge operation may be executed, thereby purging the fuel vapor canister without forcing the engine to turn on. Thus, the vehicle may be operated at peak fuel economy without increasing emissions.
In another example, a system for a plug-in hybrid electric vehicle, comprising: a fuel vapor canister coupled to a fuel tank via a fuel tank isolation valve and further coupled to atmosphere via a canister vent valve; a fuel tank pressure sensor coupled to the fuel tank; a heating element coupled to the fuel vapor canister; and a control system including executable instructions stored in non-transitory memory for: during a first condition, including an engine-off condition and the plug-in hybrid electric vehicle coupled to an external power source; heating the fuel vapor canister based on a fuel tank vacuum; opening the canister vent valve to draw atmosphere into the fuel vapor canister; and opening a fuel tank isolation valve to draw heated vapors into a fuel tank. In this way, diurnal emissions for a PHEV may be decreased. By cleaning the fuel canister of fuel vapor, there may be decreased risk of hydrocarbons bleeding out of the canister and into the atmosphere as ambient temperature decreases.
In yet another example, A method for a plug-in hybrid electric vehicle, comprising: during a first condition, including an engine-off condition, the plug-in hybrid electric vehicle coupled to an external power source, a fuel vapor canister load above a threshold, a fuel tank vacuum above a threshold, and a first ambient temperature below a threshold; heating a fuel vapor canister using power from the external power source; then opening a canister vent valve; then opening a fuel tank isolation valve. In this way, canister load may be managed without increasing the load on the PHEV battery. The external power source (e.g. a power grid) may be used to heat the fuel vapor canister in preparation for a passive purge operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.